The purpose of this project is to investigate the genetics and immunology of resistance to retroviral infection. The model I use is mice infected with muringe leukemia viruses. Both innate resistance and induced resistance are studied. Genetically defined mouse strains such as congenic, congenic recombinant, transgenic, and knockout strains are used to identify resistance genes, and to relate genetic resistance to specific immunological mechanisms. In addition, we also use these mice to investigate mechanisms of vaccine-induced protection against both acute disease and persistent retroviral infections. The work basically involves determining which types of cells are involved in protective responses versus the types of cells involved in non-protective or even harmful responses, and determining what these various cells are doing.